1In a large microwave-safe mug, add the gluten-free all-purpose flour, granulated sugar, unsweetened cocoa powder, gluten-free baking powder, and salt. Mix well to combine the dry ingredients.
Add the large egg, unsweetened almond milk, vegetable oil, and vanilla extract to the mug. Whisk thoroughly with a fork or small whisk until the batter is smooth and well combined.
Make sure to scrape the sides and bottom of the mug to incorporate all the dry ingredients.
Microwave the mug on high for 1 minute and 30 seconds to 2 minutes, or until the cake has risen and is set in the center. Cooking time may vary depending on your microwave.
Carefully remove the mug from the microwave (it will be hot). Allow the cake to cool for a minute or two before enjoying.
Optionally, top with your favorite gluten-free toppings such as berries, whipped cream, or a dusting of cocoa powder. Serve warm.